Mechanical stress detecting device

ABSTRACT

A device for detecting a mechanical stress which comprises a stock of closely laminated magnetic plates, a pair of nonmagneitc retaining plates securely mounted on both ends of the stack of the magnetic plates by means of bolts so as to form a core, four apertures extending through the core an exciting coil passing through a first pair of the apertures and a detecting coil through a second pair of the apertures, the planes of the coils being normal to each other and wherein the core has a monoaxial magnetic anisotropy established by energizing a magnetizing coil passed through said first pair of apertures while the temperature of the stack decreases from the Curie point of the magnetic material.

United States Patent 91 N ishimura [4 1 July 3,1973

[76] Inventor: Kazuo Nishimura, c/o Kabushiki Kaisha Meidensha, No.2-1-17,

Osaki, Shinagawa-ku, Tokyo, Japan [22] Filed: Nov. 13, 1970 I [21 Appl.No.: 89,175

[30] Foreign Application Priority Data Dec. 3, [969 Japan .1 44/96924Oct. 14, 1970 Japan 45/90209 [52] U.S. Cl. 73/141 A, 73/D1G. 2 [51] Int.Cl. G011 1/12 [58] Field of Search 73/DIG. 2; 336/20,

[56] References Cited UNITED STATES PATENTS 2,895,332 7/1959 Dahle etal. 73/141 A 2,569,468 10/1951 Gaugler 336/233 X 2,906,979 9/1959Bozorth 336/218 3,034,935 5/1962 Walter et al. 336/218 UX 3,125,4723/1964 Yamamoto et al. 336/218 UX 3,158,516 11/1964 Walter et al.336/218 UX 3,307,405 3/1967 Stucki 73/398 R Primary Examiner-Charles A.Ruehl Attorney-l(elman & Berman [5 7] ABSTRACT A device for detecting amechanical stress which comprises a stock of closely laminated magneticplates, a pair of non-magneitc retaining plates securely mounted on bothends of the stack of the magnetic plates by means of bolts so as to forma core, four apertures extending through the core an exciting coilpassing through a first pair of the apertures and a detecting coilthrough a second pair of the apertures, the planes of the coils beingnormal to each other and wherein the core has a monoaxial magneticanisotropy established by energizing a magnetizing coil passed throughsaid first pair of apertures while the temperature of the stackdecreases from the Curie point of the magnetic material.

4 Claims, 12 Drawing Figures MECHANICAL STRESS DETECTING DEVICE Thepresent invention relates generally to a device for detecting andmeasuring a mechanical stress or pressure and, more particularly, to adevice which is adapted to convert a mechanical stress or pressure intoa corresponding variation in an electrical quantity representative of amagnetostrictive force in a magnetic material. I

The device to which the present invention is directed is basically ofthe type which is disclosed in the Japanese Patent Publication No.31-495 issued under the date of Jan. 27, 1947. The device describedtherein comprises a plurality of closely laminated magnetic plates and apair of retaining or side plates which are securely mounted on both endsof the stack of the laminated magnetic plates by means of bolts. Themagnetic plates and the sides plates form a magnetic core. Four separateapertures extend through the magnetic core. The apertures are spaced at90 from each other so that there are two pairs of apertures which areopposite to each other. An exciting coil is passed through a first pairof opposite apertures and a detecting coil is passed through a secondpair of opposite apertures. The exciting coil and the detecting coil arethus in a crossing relationship on both sides of the magnetic core. Theexciting coil is connected to a source of an ac power. For measurementof a mechanical stress, the load is applied to the magnetic core in adirection perpendicular to the direction of thickness of the laminatedmagnetic plates, viz., at an angle of about 45 to the intersectingplanes of the exciting and detecting coils, whereby a signal having amagnitude which is indicative of the load applied to the magnetic coreis produced from the detecting coil.

The magnetic core to be used in this type of detecting device isgenerally made of a material which is magnetically non-directiveormechanically undistorted. If, in this instance, a magneticallydirective material is used, then the resultant magnetic core is mostresponsive to the applied load in the direction in which the directionof the spontaneous magnetization or of the monoaxial magnetic anisotropyis 45 to the direction of the load applied.

The material for the magnetic core is usually produced by two differentmethods, one being cold rolling and the other being cooling in amagnetic field.

The cold-rolled magnetic material is so thin that the magnetic core madeup of the laminated plates of such thin material can not be free fromdeformation due to application of a load in a direction perpendicular tothe direction in which the plates are laminated on each other. Where apair of retaining plates are secured to both ends of the stack of thelaminated magnetic plates by means of bolts or other suitable tighteningmeans, the magnetic core is subject to a mechanical distortion under thepressure exerted from the side plates. If it is desired to remove suchmechanical distortion by heating the magnetic core, the monoaxialmagnetic anistropy which has been attained through .cold rolling isimpaired and, as a result, the magnetic core is no longer acceptable foruse in the detecting device of the type to which the present inventionappertains.

When, on the other hand, a certain type of magnetic material such as forexample a sufficiently deoxidized permalloy containing about 63 percentnickel is cooled in a magnetic field to about 250 C from a temperatureapproximately the Curie point such as about 600 C, then the crystalmagnetic anistropy of the cubic crystals is caused to disappear if themagnetic material is cooled at a selected rate such as about 10 C/hourand a monoaxial magnetic anistropy is induced in the direction of themagnetic field which has been built up at the more elevated temperature.As the cooling proceeds, the individual magnetic domains are orientedand fixed in the direction of the magnetic field in which the magneticmaterial is placed. Where a plurality of magnetic plates of the thusproduced monoaxial magnetoanistropic material are laminated into aunitary block and a pair of side plates are mounted under pressure onboth sides of the block of the laminated plates so as to form anintegral magnetic core, a mechanical strain is produced in the magneticcore similarly to the magnetic core made up of laminated platesmanufactured by cold rolling.

The present invention, therefore, contemplates solving this and otherproblems and an important object of the present invention is to providea devicefor detecting a mechanical stress or pressure, wherein themagnetic plates are of considerable thickness and are sandwiched rigidlyby a pair of side plates and by bolts while internal stresses areavoided in the laminated magnetic plates. Thus, the mechanical stressdetecting device according to the present invention is robust inconstruction, economical to manufacture and simple in operation.

Another important object of the present inventionis to provide amechanical stress detecting device in which a mechanical stress orpressure is converted precisely into a corresponding variation in anelectrical quantity through utilization of the monoaxial magneticanistropy which is attained by cooling the magnetic material in amagnetic field. I

Still another important object of the present invention is to provide amechanical stress detecting device having performance characteristicswhich are so stabilized that the device can operate at all times in asatisfactory state irrespective of the variation in the load appliedthereto.

Still another object of the present invention is to prov Other objects,features and advantages of the device according to the present inventionwill be more clearly understood upon perusal of the followingdescription taken in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a perspective view of a mechanical stress detecting deviceaccording to afirst embodiment of the present invention; 1

FIG. 2 is a side elevation of a stack of magnetic plates forming part ofthe device shown in FIG. 1;

FIG. 3 is a schematic view showing an equivalent electric circuit of thedevice illustrated in FIG. 1;

FIG. 4 is a perspective view showing a magnetic core ready to be placedin a heating oven for field-cooling;

FIG. 5 is a schematic view showing the conditions in which the magneticcore shown in FIG. 4 is being cooled in a magnetic field;

FIG. 6 is a graphic view showing dc magnetization characteristics curvesof the magnetic plate produced in the cooling process of FIG. 5;

FIG. 7 is also a graphic view showing the variation in the magnetizationcharacteristics of the magnetic plate caused by application of amechanical stress to the magnetic plate;

FIG. 8 is similar to FIG. 1 but illustrates a modified form of thedevice according to this invention;

FIG. 9 is a graphic view showing a mechanical hysteresis loop of anelongation varying as a function of a mechanical stress;

FIG. 10 is a graphic view showing anelectrical hysteresis loop of anelectric output varying as a function of a mechanical stress; and

FIG. 11 and 12 are schematic views showing examples of the practicalapplication of the device according to this invention.

Reference is now made to the drawings, more specifically to FIGS. 1 and2 which show a first preferred embodiment of the present invention.

As illustrated, the device 10, includes a stack 11 of closely laminatedmagnetic plates 12 of contoured configuration. The magnetic plates 12are herein shown to have inwardly curved corners. A pair ofsubstantially identical retaining plates 13a, 13b of non-magneticmaterial are securely mounted on the first and last plates I of thestack 11 by means of suitable rigid fastening means such as bolts 14a,14b, 14c, 14d as shown. The stack 11 of the magnetic plates 12 andplates 13a, 13b attached thereto thus form a magnetic core which isgenerallyrepresented by reference numeral 15 in FIG.

The magnetic core 15 thus formed has four apertures 16a, 16b and 17a,17b which extend through the stack 11 between the plates 13a, 13b in thedirection of thickness of the plates as best seen in FIG. 4. Theapertures 16a, 16b and 17a, 1712 are symetrically spaced from each otherat an angle of about 90 and are disposed in such a manner that the two,rectangularly intersecting planes respectively defined by the pairs ofapertures are angled at about 45 to the direction in which a mechanicalstress or load P is applied to an exposed face of the magnetic core 15as indicated by an arrowhead in FIG. 1. Two separate coils 18, 19 arepassed through the respective diametrically opposite pairs of theapertures 16a, 16b and 17a, 17b. More specifically, an exciting coil 18is passed through the apertures 16a, 16b and a stress detecting coil 19is passed through the apertures 17a and 17b. The exciting and stressdetecting coils 18 and 19, respectively, thus cross each other on theouter surface of the plates 13a at an angle of about 45 to the directionof the mechanical stress or load P. Designated by reference numeral 20is a source of alternating current, which is connected to the excitingcoil 18 to energize the same.

An equivalent electric circuit of the device constructed as shown inFIG. 1 is illustrated in FIG. 3, wherein the L-shaped section 15corresponds to the magnetic core 15 which has a monoaxialmagnetoanistrophy established through cooling the magnetic core 15 in amagnetic field. The relatively broad vertical portion- 15a of theL-shaped section 15 indicates a plane of coiling established by theexciting coil 18,

which plane of coiling is identical with the magnetizing winding planebuilt up when cooling the magnetic core in a magnetic field. Themagnetic characteristics resulting from this magnetizing plane ofcoiling is indicated by a hysteresis loop a of FIG. 6 which illustratesvariations of a magnetic force H as a function of an ideal flux densityB. The relatively thin horizontal portion 15b of the L-shaped section 15in FIG. 3, on the other hand, indicates a plane of coiling establishedby the stress detecting coil 19, viz., a plane of coiling which isnormal to the magnetizing plane of coiling. The magnetic characteristicsresulting from the plane of coiling of the detecting coil 19 are lsopermcharacteristics as indicated by a hysteresis loop b of FIG. 6. v

The mechanical stress detecting device according to the presentinvention as described above is produced in the following manner. Aplurality of magnetic plates 12' are first laminated upon one anotherwith their four apertures 16a, 16b and 17a and 17b aligned. The plates13a and 13b are rigidly attached to both ends of the resultant stack 11by the aid of the bolts 14a, 14b, 14c, 14d thereby to form the magneticcore 15.

A magnetizing coil 18' is then passed through the diametrically oppositepair of apertures 16a and 16b and is connected to a dc source 21, asschematically illustrated in FIG. 4 and FIG. 5. The magnetic core 15with the magnetizing coil 18' is now placed in a heating oven 22 whichis filled with a reducing atmosphere such as hydrogen gas. Themagnetizing coil 18 is then energized from the dc source 21 with apredetermined dc magnetizing current which is independent from thethickness of the magnetic core 15, while slowly reducing the temperaturein the heating oven 22 from about 600 C through the region of about 250C at the rate of about 10 C per hours. The resultant magnetic core 15 isnow provided with a monoaxial magnetic anisotropy. This magnetic core 15is removed from the heat ing oven 22, whereupon the magnetizing coil 18'is removed from the magnetic core 15. The exciting coil 18 is nowpassedthroug h the apertures 16a, 16b on the same plane of coiling asthat of the magnetizing coil 18, while the stress detecting coil 19 ispassed through the other diametrically opposite pair of apertures 17a,

In the method for producing the device according to the presentinvention, the magnetic core 15 is annealed while being cooled in themagnetic field and the internal stress of the magnetic core is removedand the plastic deformation of the integrally combined elements of themagnetic core is caused to add to the rigidity of the core. In theprocess of cooling the magnetic core 15 in the magnetic field, monoaxialmagnetic anisotropy develops along the closed magnetic circuits 23 inthe magnetic plates 12 forming the magnetic core, as illustrated in FIG.5. The anisotropy is fixed in the magnetic core 15 as the magnetic coreis cooled down. When, therefore, the magnetic core 15 is placed on useat a normal temperature, an easy magnetization axis is established onlyin a direction parallel to the closed magnetic circuits 23 so that themagnetic core 15 is capable of sensitivity responding to a mechanicalstress or load.

FIG. 6 illustrates hysteresis loops of the magnetomotive force Hrelative to an ideal flux density B, wherein the loop a indicatesmagnetizing characteristics of the exciting coil 18 and the loop 1;indicates the magnetizing characteristics of the stress detecting coil19 in a plane perpendicular to the plane of winding of the exciting coil18. It will thus be appreciated that the cooling of the closelylaminated magnetic plates in the magnetic-field established by theclosed magnetic circuits The magnetic core thus constructed has fourapertures 16a, 16b and 17a, 17b which extend through the the laminatedmagnetic plates 12 and the loadsharing members 240 and 24b. Theapertures 16a, 16b and 17a, 17b are symmetrically spaced from each otherat an angle of about 90 and are disposed in such a manner that the twointersecting planes defined by the diametrically opposite two pairs ofthe apertures are angled at about 45 to the direction of the load P tobe When,-in the device according to the present invention, the excitingcoil 18 is energized from the ac power source with a stabilized acvoltage of a square or sinusoidal waveform and a mechanical stress isapplied to the magnetic core 15, the magnetizing characteristics of theampere-turns NI with respect to the magnetic flux (1) shifts from thesquare hysteresis loop a of FIG. 7 (which corresponds to the hysteresisloop a of FIG. 6) to the square hysteresis loop a of FIG. 7 indicated bya dotted curve. Since, however, the saturability characteristics are.practically not impaired, the magnetic core 15 can be usedsatisfactorily as a saturable reactor as will be discussed later. When,moreover, a stabilized ac voltage'having a square or sinusoidal waveformis applied to the exciting coil 18 of the device according to thepresent invention, the quantity of the flux linking the detecting coil19 during application of tion which reduces the load to be applied tothe operating electric circuit to be used in connection with thedetecting device and which provides an increased signalto-noise ratio.

When, in operation, the exciting coil 18 is excited i from the ac powersource 20. with a stabilized ac voltage having a sinusoidal or squarewaveform and the mechanical stress to be measured is applied to themagnetic core 15 in the direction P in FIG. 1, then the flux d: inducedby the current flowing through the magnetiz- I ing coil 18 is distortedand consequently caused to intersect with the stress detecting coil 19so that a voltage proportional to the applied mechanical stress isproduced by the stress detecting coil 19. The mechanical stress can bemeasured from the voltage thus obtained.

FIG. 8 now illustrates a modified form of the stress .detecting deviceaccording to the present inVention.

The modified mechanical stress detecting device 10 includes a stackll'of closely laminated magnetic plates 12 and a pair of load-sharingmembers 24a and 24b each of which is made up of a plurality of laminatedplates of a non-magnetic materialand which are mounted on both sides ofthe laminated magnetic plates. A pair of retaining plates 131., aresecurely mounted on both ends of the thus constructed stack 1 l by meansof bolts 14a, 14b, 14c, 14d as illustrated. The stack ll of thelaminated magnetic plates 12 and the load-sharing members 240 and 24bthus form a magnetic core 15. I

applied to the magnetic core 15 as indicated by an arrowhead in FIG. 8.An exciting coil 18 is passed. through one diametrically opposite pairof the aper} tures 16a, 16b and a stress detecting coil l9 is passedthrough the other diametrically opposite pair of the apertures 17a, 17b.The exciting and detecting coils 18 and 19, respectively, thus crosseach other on the outer surface of the side plate 13a at an angle ofabout 45? to the direction of the load P. The modified mechanical stressdetecting device shown in FIG. 8 is thus essentially similar to thedevice shown in FIG. 1 except for ent invention, produced in thefollowing manner." A

plurality of magnetic plates 12 are first laminated upon each other, andthe load-sharing member's 24a, 2411, much thicker than the individualplates 12, are :attached to the first and last laminated magnetic plates12 so as to form a stack 11. The retaining plates 13a and 13b are thenmounted securely on both ends of the stack 11' by means of the bolts14a, 14b, 14c, 1411, thereby constituting a magnetic core 15. Themagnetic core 15' has formed therein four apertures 16a, 16b

and 17a, 17b which are disposed in a manner previously discussed.

A magnetizing coil 18' is'passed through the diametrically opposite pairof the apertures 16a, 16b and is connected to a dc power source 21' asschematically'illustrated in FIG. 5. The magnetic core 15' thus providedwith the magnetizing coil 18' is placed in a heating oven 22 which isfilled with a suitable atmosphere such as hydrogen gas. The'magnetizingcoil 18' is then energized from-the dc power source 21 with a predeter-I mined magnetizing current which is independent from the thickness ofthe magnetic core 15', while reducing the temperature in. the heatingoven 22 through aregion of about 250 C from about 600 C preferably atthe rate of-' about 10 C per hour. The resultant mag netic core 15' hasa monoaxial magnetic anisotropy.

The magnetic core 15 'is now removed from the heat-- ing oven 22,whereupon the magnetizing coil l8 'is-removed from the magnetic core15'. The'exciting coil 18 is then passed through the apertures 16a, 16band thereafter the stress detecting coil 19 is passed'through theapertures 17a, 17b. It is apparent that the device shown in FIG. 8iscapable of detecting as a voltage signal a considerably greatermechanical stress or pressure than the device shown in FIG. 1.

For the measurement of a great mechanical stress or pressure,1it isgenerally required to use a magnetic core having a rigiditycorresponding to the magnitude of such a great mechanical stress. Toprovide the magnetic core with desired characteristics as previouslydiscussed, furthermore, the material to the usable as the magnetic coreis necessarily limited to a costly material such as for example a 63percent permalloy. The use of such a costly material in a large quantityis apparently objectionable from the economical point of view.

The provision of the load-sharing members 24a and 24b as in theembodiment shown in FIG. 8 is advantageous in this particular respectbecause only a limited number of magnetic plates 12 is used incombination with less costly non-magnetic.plates forming the loadsharingmembers 24a and 24b. The material usable as the non-magnetic plates maybe 18-8 stainless steel which is commercially readily available at a lowcost. The number of the component plates of the loadsharing members maybe selected according to the magnitude of the load to be applied to themagnetic core. The load-sharing members 24a, 24b not only reduce theproduction cost of the magnetic core but carry a portion of the loadapplied to the magnetic core so as to permit the quantitative detectionof an increased mechanical stress or pressure. In this instance, theload-sharing members 24a, 24b may be said to act as a shunt in anelectric instrument. For the measurement of a load of the order of 1tons, a corresponding number of non-magnetic plates may be combined intothe members 24a and 24b and for the measurement of a load of tons, acorrespondingly increased number of the non-magnetic plates may be used.

To save the load to be directly imparted to the laminated magneticplates 12, it may be also advantageous to have the upper and lower edgefaces of the side plates 13a, 13b flush with the exposed upper andlowerexposed faces respectively, of the stack 11', as illustrated in FIG. 8.The load to be measured is shared not only by the stack 11' but by theplates 13a, 13b so as to reduce the load to be imparted to the laminatedmagnetic plates 12. This is also desirable because the mechanicalhysteresis due to the load cycles, viz., the hysteresis of theelongation e varying with the mechanical stress 4) as shown in FIG. 9and accordingly the electrical hysteresis of the voltage output v as afunction of the load p as shown in FIG. 10 can be eliminated. Unless,therefore, the upper and lower edge faces of the plates 13a, 13b areflush with the exposed upper and lower faces,.respectively, of the stack11', then the retaining plates may not be functionally completelyintegral with the stack 11' with the result that an unusual shearingstress may be built up between the side plates 13a, 13b and the stack 11of the laminated magnetic plates 12 and the load-sharing members 24a,

24b even though the load cycles are limited within the presumed limitsof elasticity. Such unusual shearing stress will cause frictional heatbetween the plates 13a, 13b and the stack 11', resulting in themechanical and electrical hystereses as above mentioned.

The stress detecting device constructed as shown in FIGS. 1 and 8 andproviding the hereinbefore discussed outstanding features may findapplications in various fields of the industry for the purpose ofmeasuring various weights, pressures and other mechanical stresses. Onlytwo examples of such practical applications of the device according tothe invention .will be described.

First referring to FIG. 11, the mechanical stress detecting deviceaccording to the present invention is used as a saturable reactor toform part of a Royer type self-exciting transistor inverter. Theamplifier or selfexciting inverter per se is well known in the art, disclosed in the Japanese Patent Publication No. 32-4066 issued on June 22,1957. To have the device according to the present invention incorporatedin this type of self-exciting inverter, it is enough that the excitingcoil 18 be intermediately tapped and that two coils 25a, 25b for makingrespective transistors 26a, 26b alternately conductive andnon-conductive be passed through two apertures providing a plane ofcoiling which is identical with the plane of coiling of the excitingcoil 19. The transistors 26a, 26b are made alternately conductive andnonconductive so as to continuously oscillate, whereby the dc voltagesupplied from the source 27 of a stabilized dc source is converted intoan ac voltage with a square waveform through utilization of the squarehysteresis of the magnetic core 15 or 15'. The output ac voltage isdelivered from the detecting coil 19. Thus, in the arrangement of FIG.11, the ac voltage is produced through combination of a dc power sourceand two alternately operating transistors; such arrangement is thereforeconsidered to be substantially equivalent to the circuit shown in FIG.3. The self-exciting inverter shown in FIG. 11 will be used as abatterypowered portable load detector. Where, moreover, products aremoved on a belt conveyor, the flow rate of the products may be monitoredby the use of the detector constructed and arranged as illustrated inFIG. 11. If desired in this instance, a tachometric generator may becoupled with a conveyor driving motor so as to produce a signal dcvoltage which is proportional to the travelling speed of the conveyor.If this signal voltage is used as the source of a dc voltage in theinverter of FIG. 11, then a signal voltage representing the product ofthe load applied to the belt conveyor and the travelling speed of theconveyor will be produced from the detecting coil 19, thus indicatingthe flow rate of the products on the belt conveyor.

FIG. 12 illustrates another example of the practical applications of thedevice according to the present invention, wherein the device isutilized as a saturable reactor to constitute a self-feedback typemagnetic amplifier which is known per se. To use the device according tothe present invention in the magnetic amplifier of this type, a gatecoil 28 is passed through two apertures providing the same plane ofcoiling as the plane of coiling of the exciting coil 19 and the excitingand detecting coils 18 and 19 are used as reset and feedback coils,respectively. The bias magnetic field to reduce the magnetostrictivityand to increase the semistivity is determined by the ratio of turns ofthe reset (or exciting) coil 18 and the gate coil 28 and by the acvoltages supplied from the sources 29, 30, 32 of ac power. If, now, aload is imparted to the magnetic core 15 or 15', the flux produced bythe excitation of the reset coil 18 varies whereupon the ac voltageinduced in the feedback (or detecting) coil 19 is converted into a dcvoltage. The dc voltage produced in the feedback coil 19 is fed back tothe reset coil 18 so that an amplified ,voltage which is proportional tothe load detected is supplied.

Having thus described the mechanical stress detecting deviceimplementing the present invention, it will now be apparent that,according to one important aspect of the present invention, the deviceaccording to the present invention is substantially free from aninternal mechanical stress that would otherwise result from thetightening of the retaining plates on the stack of laminated plates bythe use of the bolts and nevertheless can be constructed with asufficient mechanical strength. I

Now, it should be understood that the embodiments as hereinbefore'described are merely for illustrative purposes and are not limitative ofthe present invention. Such embodiments and the practical applicationsthereof can be changed and modified in numerous manners withoutdeparting from the spirit and scope of at right angles, an exciting coilin the openings of one pair, and a detecting coil in the openings of theother pair and intersecting said exciting coil, said stack havingmonoaxial magnetic anisotropy, the improvement which comprises two loadsharing members having each a thickness substantially greater than thethick the present invention which should be interpreted from theappended claims. What is claimed is:- ,l.- In a device for converting amechanical stress to an electric quantity, the device including a stackof plates of magnetic material, tworetaining plates on the first andlast plate of said stack, elongated fastening members fixedly fasteningsaid stack between said retaining plates, whereby said retaining platesand said plates of magnetic .material constitute a continuous core, saidcore being formed with two pairs of openings extending therethrough in adirection from one retaining plate to the other retaining plate, eachpair defining a plane intersecting the plane defined by the other pairsame configuration transverse of said direction.

3. In a device as set forth in claim 1, said load sharing membersconsisting of non-magnetic material.

4. In a device as set forth in claim 1, said stack having two exposedfaces parallel to each other and to said direction, and said retainingplates having each two edge faces flush with said exposed facesrespectively.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent NO-3,742,759 Dated July 3, 1973' In'ventofls) KAZUO NISHIMURA,

It is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

In the title page, after line insert Assignee: Kabushiki KaishaMeidenshe, Tokyo, Japan Signed and sealed this 29th day ofiJanuary 1974.

(SEAL) Attest:

EDWARD M.FLETCHER,JR; RENE D. TEGTMEYER Attesting Officer 7 ActingCommissioner of Patents FORM Po-1os0 (10-69) I USCOMM-DC scan-see v I".5. GOVERNMENT PRINTING O'FFICEI IQ: 0-36633,

1. In a device for converting a mechanical stress to an electricquantity, the device including a stack of plates of magnetic material,two retaining plates on the first and last plate of said stack,elongated fastening members fixedly fastening said stack between saidretaining plates, whereby said retaining plates and said plates ofmagnetic material constitute a continuous core, said core being formedwith two pairs of openings extending therethrough in a direction fromone retaining plate to the other retaining plate, each pair defining aplane intersecting the plane defined by the other pair at right angles,an exciting coil in the openings of one pair, and a detecting coil inthe openings of the other pair and intersecting said exciting coil, saidstack having monoaxial magnetIc anisotropy, the improvement whichcomprises two load sharing members having each a thickness substantiallygreater than the thickness of each of said plates of magnetic materialand interposed between said stack and said retaining platesrespectively, said plates of magnetic material being in the fullyannealed condition and substantially free from internal stresses.
 2. Ina device as set forth in claim 1, said load sharing members eachconsisting of a plurality of plate members superposed in said direction,said plates of magnetic material and said plate members being of thesame configuration transverse of said direction.
 3. In a device as setforth in claim 1, said load sharing members consisting of non-magneticmaterial.
 4. In a device as set forth in claim 1, said stack having twoexposed faces parallel to each other and to said direction, and saidretaining plates having each two edge faces flush with said exposedfaces respectively.